PREPARATION OF D4 MOLYBDENUM OLEFIN COMPLEXES [CP(DIPHOS)MO(CO)(ETHYLENE)]+PF6- AND [CP(POM-POM)MO(CO)(ETHYLENE)]+PF6- (POM-POM = 1,2-BIS(DIMETHOXYPHOSPHINO)ETHANE) AND REACTIVITY STUDIES WITH CARBANION NUCLEOPHILES

The preparation and characterization of several novel bis phosphine-substituted d4 molybdenum-olefin complexes [Cp(diphos)Mo(CO)(ethylene)]+PF6- (3) and [Cp(Pom-Pom)Mo(CO)(ethylene)]+PF6- (4) (Pom-Pom = 1,2-bis(dimethoxyphosphino)ethane) have been carried out. Complex 3 was found to lose ethylene readily at room temperature in solution; however, complex 4 was stable for days under the same conditions. Complex 4 was further characterized by crystallographic studies. Crystal data for 4: P2(1)/c, a = 10.543 (3) angstrom, b = 12.055 (2) angstrom, c = 17.372 (5) angstrom, beta = 90.54 (3)-degrees, V = 2207.7 (11) angstrom 3, Z = 4, R(F) = 4.95%. The ethylene ligand is contained in the plane defined by the metal, the center of the Cp ligand, and the trans-phosphorus atom. The reactivity of a simple d4 molybdenum-olefin system toward nucleophilic attack was studied as a model for the phosphine-substituted systems. Thus, reaction of [CpMo(CO)3(ethylene)]+BF4- (1) with the carbanion nucleophiles Na+[CH(COOEt)2]- and Na+[CH(COOEt)(COMe)]- at -80 degrees-C gives the sigma-alkyl products Cp(CO)3MoCH2CH2CH(COOEt)2 and Cp(CO)3MoCH2CH2CH(COOEt)(COMe) in good yields. The phosphine-substituted ethylene complexes 3 and 4 also react with Na+[CH(COOEt)2]- at -78-degrees-C to give the sigma-alkyl products Cp(P-P)(CO)Mo(CH2CH2CH(COOEt)2), 10a (P-P = diphos) and 10b (P-P = Pom-Pom).